Patent Literature 1 (WO2014/203585) discloses knitting footwear comprising double-layered knitted fabrics of inner and outer layers. Here, two closed knitted fabrics are knitted from the heel to the toe and they are joined to each other at the opening of the top line. After knitting, one of the knitted fabrics is inserted into the other from the opening of the top line into the footwear comprising the double-layered knitted fabric. The footwear is manufactured seamlessly by means of a flat knitting machine, includes a small number of components, and is lightweight and thin.
Patent Literature 2 (JP2015-14058A) discloses to join the two side portions of the sole seamlessly to the side portions of the heel holding portion when a footwear is knitted on a flat knitting machine. Furthermore, Patent Literature 3 (WO 2008/143172) discloses knitting three-dimensional knitted fabric having a bottom.
There are various footwear designs. Depending on the application, thin and lightweight footwears, thick footwears with enhanced strength, and footwears with cushioning characteristics and foot supporting properties are required. Furthermore, footwears may be provided with a tongue, protrusion portions on both sides of a tongue, and a heel pocket, for example. In Patent Literature 1, a footwear of specific design can be knitted, but the method is not appropriate for knitting various footwear designs. Currently, there are knitting methods for respective basic designs such as single layered footwear or double layered footwear, and there are also knitting methods appropriate for respective local designs as to whether a tongue is provided. Such knitting methods need to be combined to a knitting method appropriate for a desired design. This work requires skill and time and is inefficient.